Nitrogenated carbon electrode for chalcogenide device and method of making same

ABSTRACT

A nitrogenated carbon electrode suitable for use in a chalcogenide device and method of making the same are described. The electrode comprises nitrogenated carbon and is in electrical communication with a chalcogenide material. The nitrogenated carbon material may be produced by combining nitrogen and vaporized carbon in a physical vapor deposition process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/448,184, entitled “Nitrogenated Carbon Electrode for ChalcogenideDevice and Method of Making Same” and filed on Jun. 7, 2006 now U.S.Pat. No. 7,473,950; the disclosure of which is hereby incorporated byreference herein.

FIELD OF INVENTION

The present invention relates generally to electronic devices utilizingchalcogenide materials. In particular, the present invention relates toa composition for an electrode of a chalcogenide electronic device.

BACKGROUND OF THE INVENTION

Non-volatile memory devices are used in certain applications where datamust be retained when power is disconnected. Applications generallyinclude memory cards, consumer electronics (e.g., digital cameramemory), automotive (e.g., electronic odometers), and industrialapplications (e.g., electronic valve parameter storage). Non-volatilememories may use phase-change memory materials, e.g., materials that canbe programmed between a generally amorphous and a generally crystallinestate, for electronic memory applications. This type of memory generallyincludes an array of memory elements, wherein each memory elementdefines a discrete memory location. Each memory element may include avolume of phase-change material and at least one electrode.

One type of known memory element utilizes a phase-change material thatmay be programmed between a generally amorphous state and generallycrystalline local order. In addition, the phase-change material may beprogrammed between different detectable states of local order across theentire spectrum between a completely amorphous state and a completelycrystalline state. These different structured states have differentvalues of resistivity, and therefore each state can be determined byelectrical sensing. Typical materials suitable for such applicationinclude those utilizing various chalcogenide materials. Unlike certainknown devices, these electrical memory devices typically do not usefield effect transistor devices as the memory storage element, but maycomprise, in the electrical context, a monolithic body of thin filmchalcogenide material. As a result, very little chip real estate isrequired to store a bit of information, thereby providing for inherentlyhigh density memory chips.

One characteristic common to both solid state and phase-change memorydevices is significant power consumption, particularly when setting orreprogramming memory elements. Generally, the electrical energy requiredto produce a detectable change in resistance in these materials isapproximately 100 picojoules. This amount of energy must be delivered toeach of the memory elements in the solid state matrix of rows andcolumns of memory cells. Such high energy requirements translate intohigh current carrying requirements for address lines and cellisolation/access devices that are associated with each discrete memoryelement. Electrodes (also referred to as electrical contacts) used tosupply heat to the phase-change memory material can also have asignificant effect on these energy requirements. Generally, higherresistivity electrodes will generate more heat and reduce energyconsumption.

Another characteristic common to both solid state and phase-changememory devices is that both have a limited reprogrammable cycle life,i.e., the number of times the device can be programmed from an amorphousstate to a crystalline state, and vice versa. Further, over time thephase-change memory material can fail to reliably reprogram between anamorphous and crystalline state. Instability in the resistivity of theelectrical contacts or electrodes used to supply heat to thephase-change memory material can exacerbate this reliability problem. Itwould be advantageous to increase the programmable cycle life of aphase-change memory material and to improve the reliability andstability of the memory devices incorporating them.

A disadvantage of known electrodes used with phase-change memory devicesis that the electrodes tend to be chemically reactive with theirassociated phase-change material. This reactivity degrades theperformance of the memory device and results in delamination ofphase-change material or in a chemical compositional change to thephase-change material, which can adversely affect the device memorycharacteristics.

In addition, certain known electrodes used in memory devices havesurfaces that are textured, uneven, or rough. Relatively thin layers (onthe order of Angstroms) of insulators, electrodes, and phase-changememory materials are typically used in memory devices. Thus, an unevenelectrode surface can cause the electrode to protrude through a portionof the phase-change chalcogenide material, resulting in an adverseimpact on its memory characteristics.

Thus a need has arisen for an electrode and memory device that addressesone or more of the foregoing disadvantages.

SUMMARY OF THE INVENTION

An embodiment of the present invention is an electronic device thatcomprises an electrode in electrical communication with a phase-changememory material, wherein the electrode comprises nitrogenated carbon.The electronic device may be a memory device. In one embodiment, theelectrode consists essentially of nitrogenated carbon. In oneembodiment, the nitrogenated carbon electrode is prepared by mixingnitrogen and vaporized carbon. In another embodiment, the vaporizedcarbon is produced by sputtering. In still another embodiment, thephase-change material is a chalcogenide material.

Another embodiment of the invention is an electronic device, comprising:a chalcogenide material; and an electrode in electrical communicationwith said chalcogenide material, said electrode comprising nitrogenatedcarbon. The electronic device may be a memory device. The electronicdevice may be a threshold switch.

Another embodiment of the invention is an electronic device, comprising:a threshold switching material; and an electrode in electricalcommunication with the threshold switching material. The thresholdswitching material may be an S-type threshold switching material. Theelectronic device may be a threshold switch.

Another embodiment of the invention is an electronic device, comprising:a programmable resistance material; and a nitrogenated carbon materialin electrical communication with the programmable resistance material.The electronic device may be a memory device. The programmableresistance material may comprise a phase-change material. Theprogrammable resistance material may comprise a chalcogenide material.

Another embodiment of the invention is an electronic device, comprising:a chalcogenide material; and a nitrogenated carbon material inelectrical communication with the chalcogenide material. The electronicdevice may be a memory device. The electronic device may be a thresholdswitch.

Another embodiment of the invention is an electronic device, comprising:a threshold switching material; and a nitrogenated carbon material inelectrical communication with the threshold switching material. Thethreshold switching material may be an S-type threshold switchingmaterial. The electronic device may be a threshold switch.

Another embodiment of the invention is an electronic device, comprising:a phase-change material; and a first material in communication with thephase-change material, the first material consisting essentially ofcarbon and nitrogen. The communication may include electricalcommunication. The communication may include thermal communication. Theelectronic device may be a memory device.

Another embodiment of the invention is an electronic device, comprising:a chalcogenide material; and a first material in electricalcommunication with the chalcogenide material, the first materialconsisting essentially of carbon and nitrogen. The electronic device maybe a memory device. The electronic device may be a threshold switch.

Another embodiment of the invention is a method of making an electronicdevice, the method comprising: forming a nitrogenated carbon material;and forming a phase-change material, the phase-change material being inelectrical communication with the nitrogenated carbon material. Theelectronic device may be a memory device.

Another embodiment of the invention is an electronic device, comprising:a threshold switching material; and a first material in electricalcommunication with the threshold switching material, the first materialconsisting essentially of carbon and nitrogen. The threshold switchingmaterial may be an S-type threshold switching material. The electronicdevice may be a threshold switch.

Another embodiment of the invention is a method of making an electronicdevice, the method comprising: forming a nitrogenated carbon material;and forming a chalcogenide material, the chalcogenide material being inelectrical communication with the nitrogenated carbon material. Thechalcogenide material may be a phase-change material. The chalcogenidematerial may be a threshold switching material. The electronic devicemay be memory device. The electronic device may be a threshold switch.

Another embodiment of the invention is a method of making an electronicdevice having an electrode, the method comprising providing a substrate,and mixing nitrogen gas with vaporized carbon, thereby forming theelectrode on the substrate. In one embodiment, the method furthercomprises depositing a phase-change memory material on the electrode. Inanother electrode, the method further comprises depositing a thresholdswitching material on the electrode. The threshold switching materialmay be an S-type threshold switching material. The threshold switchingmaterial may be a chalcogenide threshold switching material. In anotherembodiment, the method further comprises depositing a chalcogenidematerial on the electrode. In another embodiment, the method furthercomprises sputtering a carbon target to produce the vaporized carbon. Inyet another embodiment, the sputtering of a carbon target includescontacting the carbon target with an ionized gas, wherein the volumeratio of nitrogen gas to ionized gas is approximately thirty to seventypercent. In yet another embodiment, the electrode is a first electrodeand the method further comprises depositing a second electrode on thephase-change memory material. In some embodiments, this second electrodemay also comprise nitrogenated carbon. Thus, memory devices may be builtwith either the first electrode, second electrode, or both comprisingnitrogenated carbon.

BRIEF DESCRIPTION OF THE DRAWINGS

The present embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is an exemplary embodiment of a memory element used to illustratean embodiment of an electrode in accordance with the present invention;

FIG. 2 is a flow chart of a method for making a memory element accordingto an embodiment;

FIG. 3 is a flow chart of a method for making a nitrogenated carbonelectrode according to an embodiment;

FIG. 4 is an exemplary embodiment of a threshold switch; and

FIG. 5 is an example of the current-voltage characteristics of achalcogenide threshold switch.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Although this invention will be described in terms of certain preferredembodiments, other embodiments that are apparent to those of ordinaryskill in the art, including embodiments that do not provide all of thebenefits and features set forth herein, are also within the scope ofthis invention. Accordingly, the scope of the invention is defined onlyby reference to the appended claims.

A memory device having a nitrogenated carbon electrode in electricalcommunication with a phase-change memory material is provided. Theelectrode may be prepared by combining a variable amount of nitrogenwith vaporized carbon. The vaporized carbon may be generated using aphysical vapor deposition process. In comparison to an electrodecomprising only carbon, the nitrogenated carbon electrode may providefor improved resistivity, surface smoothness, and electrical resistivitystability.

FIG. 1 illustrates an exemplary embodiment of a memory element 10 havinga discrete memory location, which may be incorporated into a memorydevice. As understood by one skilled in the art, the specific structureand configuration of components with respect to memory element 10 mayvary depending upon the desired design characteristics of a particularmemory device. Accordingly, the specific structure of memory element 10,as shown in FIG. 1, is intended to be exemplary.

Memory element 10 includes a bottom electrode 22 in electricalcommunication with a phase-change memory material 26. In one or moreembodiments of the invention, the phase-change memory material may beprogrammed between two or more phases or structural states that havedistinct electrical characteristics. Phase-change memory material 26 mayinclude one or more chalcogen elements. The chalcogen elements may beeither Te and Se. The phase-change material may further include one ormore elements selected from the group consisting of Ge, Sb, Bi, Pb, Sn,As, S, Si, P, O, N, In, and mixtures thereof. Suitable phase-changematerials include, but are not limited to, GaSb, InSb, InSe, Sb₂Te₃,GeTe, Ge₂Sb₂Te₅, InSbTe, GaSeTe, SnSb₂Te₄, InSbGe, AgInSbTe, (GeSn)SbTe,GeSb(SeTe), and Te₈₁Ge₁₅Sb₂S₂. A material that includes one or morechalcogen elements is referred to as a chalcogenide material.

The resistivity of chalcogenides generally varies by two or more ordersof magnitude when the chalcogenide material changes phase from anamorphous state (more resistive) to a polycrystalline state (lessresistive). In memory devices such as those incorporating the memoryelement 10 of FIG. 1, the electrodes deliver an electrical current tothe phase-change memory material 26. As the electrical current passesthrough memory element 10, at least a portion of the electrical energymay be transferred to the surrounding material as heat. The electricalenergy may be converted to heat energy via Joule heating. The amount ofelectrical energy converted to heat energy is a function of theresistivities of the electrodes and the memory material as well as thecurrent density passing through the electrodes and the memory material.

Referring to FIG. 1, bottom electrode 22 supplies energy (e.g.electrical energy and/or heat energy) to change the state ofphase-change memory material 26. Phase-change memory material 26 andbottom electrode 22 may be selected to meet the particular energyrequirements of a device incorporating memory element 10. To providepredictable and stable operation of memory element 10, bottom electrode22 may be selected to have a substantially stable resistivity overtemperatures ranging from about 0° C. to about 700° C. Bottom electrode22 may also be selected to be minimally chemically reactive withphase-change memory material 26 over this temperature range.

Referring to FIG. 1, thicknesses for bottom electrode 22 andphase-change memory material 26 may range from about 200 to 1000Angstroms. The surface of bottom electrode 22 may be uniform and smoothso as to minimize the development of peaks that can partially protrudethrough phase-change memory material 26 in contact region 32, causing anadverse impact on the memory characteristics of the device. Similarly,it is desirable to avoid peaks that protrude through phase-change memorymaterial 26 into a top electrode 28, which can result in a shortcircuit. Bottom electrode 22 may be constructed from a variety ofmaterials. For example, bottom electrode 22 may be formed of one or moreconductive materials. In an embodiment of the present invention, bottomelectrode 22 comprises a nitrogenated carbon material. In anotherembodiment of present invention, bottom electrode 22 consistsessentially of a nitrogenated carbon material.

An insulator 20 may be provided below bottom electrode 22. Insulator 20is generally a dielectric material such as SiO₂, and may be deposited ona substrate (not shown) using a process such as chemical vapordeposition (CVD). The substrate is generally a semiconductor materiallike silicon. However, other substrates including, but not limited to,those containing ceramic material, organic material, or glass materialas part of the infrastructure are also suitable.

Memory element 10 further includes top electrode 28 in electricalcommunication with phase-change memory material 26. Like bottomelectrode 22, top electrode 28 may be prepared from a variety of knownelectrode materials. For example, top electrode 28 may be formed of oneor more conductive materials. In an embodiment of the present invention,top electrode 28 comprises a nitrogenated carbon material. In anotherembodiment of the invention, top electrode 28 consists essentially of anitrogenated carbon material. Insulator 30 may also be provided abovetop electrode 28, as shown in FIG. 1.

FIG. 2 illustrates a flow diagram of an exemplary method for makingmemory element 10 of FIG. 1. At step 110, insulator 20 is deposited ontoa substrate (not shown) such as a semiconductor or other known substrateusing a process such as CVD. At steps 112 and 114, bottom electrode 22is formed and subsequently masked and etched to form opening 34.Insulator 24 is then deposited at step 116 onto bottom electrode 22using known deposition techniques such as CVD. Insulator 24 is maskedand etched at step 118 to create opening 33. At step 119 a portion ofphase-change memory material 26 is deposited onto insulator 24 and intoopening 33 using physical vapor deposition (PVD) techniques. As shown inFIG. 1, contact area 32 is created at the interface of phase-changememory material 26 and bottom electrode 22. The size of contact area 32and the corresponding opening 33 are directly proportional to therequired amount of phase-change memory material 26. Therefore, byreducing the size of contact area 32, the required volume ofphase-change memory material 26 in opening 33 is reduced, therebyreducing the total current needed to program the memory device. In anexemplary embodiment, the contact area 32 is less than approximately0.005 micron². In another embodiment, the contact area 32 is less thanapproximately 0.0025 micron².

Referring again to FIG. 2, top electrode 28 is deposited at step 120onto phase-change memory material 26. At step 122 the stack ofphase-change material 26 and top electrode 28 are masked andconcurrently etched to create windows 36 and 38. Finally, top insulator30 is deposited at step 124 onto top electrode 28 such that it fillswindows 36 and 38. Top electrode 28 may be formed of one or moreconductive materials. Top electrode 28 may include materials such asTiW, TiAIN, carbon, and TiSiN. In an embodiment of the presentinvention, top electrode 28 comprises a nitrogenated carbon which may beprepared in accordance with a sputtering method as described below withrespect to both bottom electrode 22 and top electrode 28. In anotherembodiment of the present invention, top electrode 28 consistsessentially of a nitrogenated carbon which may be prepared in accordancewith a sputtering method as described below with respect to both bottomelectrode 22 and top electrode 28.

In one embodiment of the present invention, it is possible that bottomelectrode 22 (but not top electrode 28) comprises or consistsessentially of a nitrogenated carbon material. In another embodiment ofthe invention, it is possible that top electrode 28 (but not bottomelectrode 22) comprises or consists essentially of a nitrogenated carbonmaterial. In another embodiment of the present invention, it is possiblethat both bottom electrode 22 and top electrode 28 comprise or consistessentially of a nitrogenated carbon material.

In the embodiment shown in FIG. 1, the bottom electrode 22 and the topelectrode 28 are in direct physical contact with the phase-changematerial. In other embodiments of the invention, the bottom electrodeand/or the top electrode may not be in direct physical contact with thephase-change material. Also, the carbonated nitride material of thebottom electrode 22 may or may not be in direct physical contact withthe phase-change material. Also, the carbonated nitride material of thetop electrode 28 may or may not be in direct physical contact with thephase-change material.

FIG. 3 shows a flow diagram illustrating an exemplary method for makingbottom electrode 22 and/or top electrode 28. In steps 200 and 202 apyrolytic graphite target is placed in a PVD vacuum chamber along withthe substrate (on which insulator 20 has been previously deposited). Apotential difference is applied at step 204 to the carbon target and thesubstrate/insulator 20 combination. As with known PVD processes, thepower density (i.e. power divided by the surface area of the sputteredtarget in W/sq. in target area) may be adjusted. As the power density isincreased, the rate of carbon vaporization and rate of deposition on thesubstrate also increases. The power density may range from about 20 toabout 40 W/sq. in.

An ionizing gas such as, but not limited to, argon is fed into a PVDvacuum chamber at step 206. By applying the potential difference in thevacuum chamber at step 208, a plasma is initiated in which the argon gasis ionized and charged. In this way, the argon ions collide with thecarbon target, releasing carbon atoms into a vapor phase. The flow rateof argon is preferably used to control the pressure in the PVD chamber.As the pressure of the argon gas increases, the amount of ionized argonavailable to collide with the carbon target generally increases, whichincreases the vaporization of carbon and its deposition rate onto thesubstrate. Pressures used in accordance with this embodiment generallyrange from about 1 to 10 milliTorr, with pressures from about 2 to 8milliTorr being preferred. The deposition process continues until thedesired electrode thickness is obtained at step 210.

For electrodes 22, 28 comprising nitrogenated carbon, step 206 furtherincludes introducing nitrogen gas into the PVD chamber with the argon.The introduction of nitrogen provides an electrode with an increased andmore stable resistivity than carbon alone. In addition, the relativefeed rates of nitrogen and argon affect the resistivity of the resultingelectrode and the sensitivity of the resistivity to changes intemperature. In accordance with this embodiment, nitrogen is generallyfed into the vacuum chamber at a volumetric flow rate of approximatelythirty to seventy percent of the volumetric flow rate of argon. In analternative embodiment, the volumetric flow rate of nitrogen is aboutsixty percent of the volumetric flow rate of argon.

In comparison to known carbon electrodes, the nitrogenated carbonelectrodes prepared in accordance with the foregoing methods may exhibitimproved surface smoothness, higher resistivity, and more stableresistivity with temperature variation. Further, electrodes such asthose described herein may be subjected to further processing, such asrapid thermal annealing. Unlike pure carbon electrodes, electrodesprepared in accordance with the foregoing methods may maintainrelatively higher resistivities even after annealing at temperaturesfrom about 400° C. to about 700° C.

Referring again to FIG. 1, bottom electrode 22 and/or top electrode 28may comprise a nitrogenated carbon material. If both the bottom and topelectrodes comprise a nitrogenated carbon material, then thenitrogenated carbon material of the bottom electrode may be the same asor may be different from the nitrogenated carbon material of the topelectrode. Hence, the nitrogenated carbon material of the bottomelectrode and the nitrogenated carbon material of the top electrode mayhave the same composition or they may have different compositions.

The nitrogenated carbon material of the bottom electrode and/or topelectrode may be prepared by combining nitrogen gas and vaporizedcarbon. The carbon component used to form the electrodes may bevaporized by a variety of known techniques, such as physical vapordeposition (PVD), chemical vapor deposition (CVD), and plasma enhancedCVD. However, it is preferably vaporized by sputtering a carbon targetwith an ionized gas in accordance with the preceding method. Becauseelectrode 22 and/or electrode 28 are deposition products formed bymixing nitrogen gas and vaporized carbon, they may have a substantiallyuniform composition along its thickness, resulting in generally uniformelectrical characteristics throughout.

With respect to the method of FIG. 3, the relative feed rates ofnitrogen and argon in a carbon sputtering process can have an effect onthe resistivity of the resulting electrode. To illustrate this effect,several examples of electrodes prepared in accordance with the foregoingmethods will now be described. Each of the electrodes was prepared bysputtering a 75 sq. in. pyrolytic graphite target with argon. Powerdensity was held constant at 27 Watt/sq. in. Pressure was maintained at2 milliTorr, and the argon flow rate was held at 20 standard cubiccentimeters per minute. Starting with pure carbon as a control, a seriesof electrodes was prepared by adding various flow rates of nitrogen tothe PVD chamber. Electrode resistivities were measured in theas-deposited state and after rapid thermal annealing for one minute at450° C., 500° C., and 700° C. each. The results are set forth below inTable 1.

TABLE 1 Resistivities (ohm-cm) N₂/Argon volumetric ratio (sccm/sccm) ×100 (%) As-deposited 450° C. 500° C. 700° C. 0 0.696 0.0319 0.02120.00595 10 0.3360 0.0289 0.0213 0.00779 20 0.174 0.0275 0.027 0.0135 300.690 0.118 0.0954 0.0516 40 0.662 0.266 0.0984 0.0867 50 2.27 0.5360.439 0.293 60 1.30 0.354 0.302 0.325

As the data indicates, after annealing, the electrode made with purecarbon (i.e., 0% nitrogen) experienced a significant drop inresistivity. Its resistivity also showed a greater than 80 percent dropas the annealing temperature was varied from 450° C. to 700° C. Incontrast, the nitrogenated electrodes showed a more stable resistivitywhen subjected to the various annealing temperatures, with the 60%nitrogen/argon electrode yielding a resistivity percentage change ofonly about 8 percent between 450° C. and 700° C.

In another embodiment of the invention, an electrode comprisingnitrogenated carbon (or consisting essentially of nitrogenated carbon)may be prepared by sputtering (e.g. physical vapor deposition) a targetcomprising both carbon and nitrogen. In an embodiment of the invention,an electrode may be formed by sputtering a target that consistsessentially of the elements carbon and nitrogen. In one embodiment ofthe invention, the atomic percent of the carbon (of the target) may begreater than the atomic percent of the nitrogen (of the target). In anembodiment, the atomic percent of the carbon may be greater than about50% while the atomic percent of the nitrogen may be less than about 50%.In another embodiment, the atomic percent of the carbon may be greaterthan or equal to about 60% while the atomic percent of the nitrogen maybe less than or equal to about 40%. In another embodiment, the atomicpercent of the carbon may be greater than or equal to about 70% whilethe atomic percent of the nitrogen may be less than or equal to about30%. In another embodiment, the atomic percent of the carbon may begreater than or equal to about 80% while the atomic percent of thenitrogen may be less than or equal to about 20%. In another embodiment,the atomic percent of the carbon may be greater than or equal to about85% while the atomic percent of the nitrogen may be less than or equalto about 15%. In another embodiment, the atomic percent of the carbonmay be greater than or equal to about 90% while the atomic percent ofthe nitrogen may be less than or equal to about 10%. In an embodiment,the atomic percent of the carbon may be greater than or equal to about95% while the atomic percent of the nitrogen may be less than or equalto about 5%. In another embodiment, the atomic percent of the carbon maybe between about 90% and 95% while the atomic percent of the nitrogenmay be between about 10% and 5%. In one example, the target consistsessentially of carbon and nitrogen where the atomic percent of carbon isabout 93% while the atomic percent of nitrogen is about 7%. In anembodiment of the invention, the target may comprise a carbon nitridematerial. In an embodiment of the invention, the target may consistessentially of a carbon nitride material.

Referring again to FIG. 1, in one or more embodiments of the invention,electrode 22 and/or the electrode 28 may comprise an electrode materialwherein the electrode material consists essentially of the elementscarbon and nitrogen. In one or more additional embodiments of theinvention, electrode 22 and/or the electrode 28 may consist essentiallyof an electrode material wherein the electrode material consistsessentially of the elements carbon and nitrogen. For example, electrode22 (and/or electrode 28) may be formed as a layer of electrode materialwhere the electrode material consists essentially of the elements carbonand nitrogen. In one embodiment of the invention, the atomic percent ofthe carbon (of the electrode material) may be greater than the atomicpercent of the nitrogen (of the electrode material). In an embodiment,the atomic percent of the carbon may be greater than about 50% while theatomic percent of the nitrogen may be less than about 50%. In anotherembodiment, the atomic percent of the carbon may be greater than orequal to about 60% while the atomic percent of the nitrogen may be lessthan or equal to about 40%. In another embodiment, the atomic percent ofthe carbon may be greater than or equal to about 70% while the atomicpercent of the nitrogen may be less than or equal to about 30%. Inanother embodiment, the atomic percent of the carbon may be greater thanor equal to about 80% while the atomic percent of the nitrogen may beless than or equal to about 20%. In another embodiment, the atomicpercent of the carbon may be greater or equal to about 90% while theatomic percent of the nitrogen may be less than or equal to about 10%.In another embodiment, the atomic percent of the carbon may be greaterthan or equal to about 95% while the atomic percent of the carbon may beless than or equal to about 5%. In another embodiment, the atomicpercent of the nitrogen may be greater than about 5% while the atomicpercent of the carbon is less than 95%. In another embodiment, theatomic percent of the carbon may be between about 90% and 95% while theatomic percent of the nitrogen may be between about 10% and 5%. In oneexample, the electrode material consists essentially of carbon andnitrogen where the atomic percent of the carbon is about 93% while theatomic percent of the nitrogen is about 7%. It is noted that increasingthe atomic percent of the nitrogen may increase the resistivity of theelectrode material while decreasing the atomic percent of the nitrogenmay decrease the resistivity of the electrode material.

In an embodiment of the invention, the electrode material may be acarbon nitride material. Hence, in an embodiment of the invention, atleast one of the electrodes of the memory device (for example, electrode22 and/or electrode 28 shown in FIG. 1) may comprise a carbon nitridematerial. In another embodiment of the invention, at least one of theelectrodes of the memory device (for example, electrode 22 and/orelectrode 28 shown in FIG. 1) may consist essentially of a carbonnitride material. As an example, electrode 22 and/or electrode 28 may beformed as a layer of carbon nitride material.

In an embodiment of the invention, an electrode material consistingessentially of carbon and nitrogen may be in direct physical contactwith the phase-change material. In another embodiment of the invention,an electrode material consisting essentially of carbon and nitrogen maybe in electrical communication with the phase-change material but not bein direct physical contact with the phase-change material.

Additional conceivable device structures are described, withoutlimitation, in U.S. Pat. No. RE 37,259, U.S. Pat. No. 6,031,287, U.S.Pat. No. 6,617,192, U.S. Pat. No. 6,943,365, U.S. Pat. No. 6,969,866,U.S. Pat. No. 6,969,869 and U.S. Pat. No. 6,972,428 which are all herebyincorporated by reference herein.

The electrodes and electrode materials described herein (as well as themethods for preparing the electrodes and electrode materials asdescribed herein) may be used in combination with any programmableresistance material capable of being programmed between two or moreresistance states. In one embodiment, the programmable resistancematerial may be a phase-change material. In another embodiment of theinvention, the programmable resistance material may not be aphase-change material. In an embodiment of the invention, theprogrammable resistance material may be programmed among three or moreresistance states.

The electrodes and the electrode materials described herein (as well asthe methods for making the electrodes and electrode materials describedherein) may be used in combination with threshold switching materials toform threshold switches. Examples of threshold switching materialsinclude chalcogenide threshold switching materials. An example of achalcogenide threshold switching material is the alloy Si₁₄Te₃₉As₃₇Ge₉X₁where X may, for example, be the element In (indium) or the element P(phosphorous). In one or more embodiments of the invention, thechalcogenide threshold switching material is in an amorphous state. Inone or more embodiments of the invention, the chalcogenide thresholdswitching material does not crystallize with the addition of energy. Inone or more embodiments of the invention, the chalcogenide thresholdswitching material is not a phase-change material.

The chalcogenide threshold switching material may be used in combinationwith one or more electrodes (preferably two or more electrodes) to forma chalcogenide threshold switch (also referred to as a chalcogenidethreshold switching device or a chalcogenide threshold switchingelement).

An example of a chalcogenide threshold switch using two electrodes isshown in FIG. 4. FIG. 4 shows a chalcogenide threshold switch 300comprising a bottom electrode 320 a, a chalcogenide threshold switchingmaterial 330 and a top electrode 320 b. The bottom electrode is formedover a substrate 310. A dielectric material 325 is formed over thebottom electrode 320 a. An opening 327 is formed in dielectric bottomelectrode 320 a and a top electrode 320 b formed over the chalcogenidethreshold switching material 330. The threshold switch 300 is formedover a substrate 310. A threshold switch using two electrodes may bereferred to as a two terminal threshold switch. In other embodiments ofthe invention, it is conceivable that the chalcogenide threshold switchhas more than two electrodes.

Associated with a chalcogenide threshold switch is a current-voltage, or“I-V”, characteristic curve. The I-V characteristic curve describes therelationship between the current through the threshold switch as afunction of the voltage across the threshold switch.

An example of an I-V characteristic curve for a chalcogenide thresholdswitch (such as a two terminal chalcogenide threshold switch) is shownin FIG. 5. FIG. 5 shows the I-V plot in both the first quadrant (wherevoltages and currents are positive) and the third quadrant (wherevoltages and currents are negative). While only the first quadrant isdescribed below, an analogous description applies to the curve in thethird quadrant of the I-V plot (where the voltage and the current areboth negative).

The I-V characteristic curve includes an “off-state” branch 450 and an“on-state” branch 460. The off-state branch 450 corresponds to thebranch in which the current passing through the threshold switchincreases slightly upon increasing the voltage applied across thethreshold switch. This branch exhibits a small slope in the I-V plot andappears as a nearly horizontal line in the first (and third) quadrant ofFIG. 5. The on-state branch 460 corresponds to the branch in which thecurrent passing through the threshold switch increases significantlyupon increasing the voltage applied across the threshold switch. Themagnitude of the slope of the on-state branch is greater than themagnitude of the slope of the off-state branch. In the example shown inFIG. 5, the on-state branch exhibits a large slope in the I-V plot andappears as a substantially vertical line in the first (and third)quadrant of FIG. 5. The slopes of the off-state and on-state branchesshown in FIG. 5 are illustrative and not intended to be limiting.Regardless of the actual slopes, the on-state branch exhibits a steeperslope than the off-state branch. Hence, the off-state branch correspondsto a relatively high resistance condition of the threshold switch. Theon-state branch corresponds to a relatively low resistance condition ofthe threshold switch.

When conditions are such that the current through the threshold switchand voltage across the switch is described by a point on the off-statebranch of the I-V curve, the threshold switch is said to be in the “OFF”state. Likewise, when conditions are such that the current through thethreshold switch and voltage across the threshold switch is described bya point on the on-state branch of the I-V curve, the threshold switch issaid to be in the “ON” state. The resistance of the threshold switch inthe OFF state is higher than the resistance of the threshold switch inthe ON state.

The switching properties of the threshold switch can be described byreference to FIG. 5. When no voltage is applied across the thresholdswitch, the threshold switch is in the “OFF” state and no current flows.This condition corresponds to the origin of the I-V plot shown in FIG. 5(current=0, voltage=0). The threshold switch remains in the OFF state asthe voltage across the threshold switch and the current through thethreshold switch is increased, up to a voltage V_(th) which is referredto as the “threshold voltage” of the threshold switch. When the voltageacross the threshold switch is less than V_(th), the slope of theoff-state branch of the I-V curve is small and the current flowingthrough the threshold switch increases only in a small amount as theapplied voltage is increased. It is noted that the current I_(th) isreferred to as the threshold current and is the current that correspondsto the threshold voltage.

When the applied voltage across the threshold switch equals or exceedsthe threshold voltage V_(th), the threshold switch switches from theoff-state branch 450 to the on-state branch 460 of the I-V curve. Theswitching event occurs instantaneously and is depicted by the dashedline in FIG. 5. Upon switching, the voltage across the threshold switchdecreases significantly and the current through the threshold switchbecomes much more sensitive to changes in the device voltage (hence,branch 460 is steeper than branch 450). The threshold switch remains inthe on-state branch 460 as long as a minimum current, labeled I_(h) inFIG. 5, is maintained. I_(h) is referred to as the holding current ofthe threshold switch and the associated voltage V_(h) is referred to asthe holding voltage of the threshold switch. If the threshold switchconditions are changed so that the current becomes less than I_(h), thethreshold switch normally returns to the off-state branch 450 of the I-Vplot and requires re-application of a voltage which is greater than orequal to the threshold voltage V_(th) to resume operation on theon-state branch. If the current is only momentarily (a time less thanthe recovery time of the chalcogenide threshold switching material)reduced below I_(h), the ON state of the threshold switch may berecovered upon restoring the current through the threshold switch whichis at or above I_(h).

Analogous switching behavior occurs in the third quadrant of the I-Vplot shown in FIG. 5. Provided one is aware of the negative polaritiesof both the voltage and current of the I-V curve in the third quadrant,the switching behavior in the third quadrant is analogous to thatdescribed hereinabove for the first quadrant. For example, appliedvoltages having a magnitude greater than the magnitude of the negativethreshold voltage in the third quadrant induce switching from theoff-state branch 450 to the on-state branch 460.

Hence, as described above, the chalcogenide threshold switch may beswitched from an OFF state to an ON state by application of a voltageacross the threshold switch having a magnitude which is greater than orequal to the magnitude of the threshold voltage V_(th). While notwishing to be bound by theory, it is believed that application of avoltage across the threshold switch which is at or above the thresholdvoltage may cause the formation of a conductive channel or filamentwithin the threshold switching material. At the threshold voltageV_(th), the electric field experienced by the threshold switchingmaterial is sufficiently high to induce a breakdown or avalanche effectwhereby electrons are removed from atoms to form a highly conductive,plasma-like filament of charge carriers. Rather than being bound toatoms, some electrons become unbound and highly mobile. As a result, aconductive channel or filament forms. The conductive filamentconstitutes a conductive volume within the otherwise resistivechalcogenide threshold switching material. The conductive filamentextends through the chalcogenide threshold switching material andprovides a low resistance pathway for electrical current. Portions ofthe chalcogenide material outside of the filament remain resistive.Since electric current traverses the path of least resistance, thepresence of a conductive filament renders the chalcogenide thresholdswitching material more conductive and establishes an “ON” state. Thecreation of a conductive filament is the event that underlies theswitching of the threshold switch from its OFF state to its ON state.

It is noted that in one or more embodiments of the invention, thechalcogenide threshold switching material (which may be in an amorphousstate) does not crystallize with the addition of energy. In one or moreembodiments of the invention, the threshold switching material is not aphase-change material.

It is noted that the current-voltage characteristic curve shown in FIG.5 is an example of an S-type current-voltage characteristic curve. Athreshold switch exhibiting this current-voltage behavior is referred toas an S-type threshold switch. Likewise, the corresponding thresholdswitching material is referred to as S-type threshold switchingmaterial. It is possible that any threshold switching material thatexhibits similar S-type current-voltage characteristics may be used asthe threshold switching material. In one embodiment, the S-typethreshold switching material may be chalcogenide material. In anotherembodiment, the S-type threshold switching material may not be achalcogenide material.

All of the electrode materials described herein may be used for anelectrode of a threshold switch (such as a chalcogenide threshold switchor an S-type threshold switch). The disclosure herein with regards tothe composition of electrodes 22 and 28 shown in FIG. 1 is applicable toelectrodes used for threshold switches (such as chalcogenide thresholdswitches and S-type threshold switches).

Referring again to FIG. 4, it is noted that electrode 320 a and/orelectrode 320 b may be formed of any of the electrode materialsdescribed herein. For example, in one or more embodiments of theinvention, electrode 320 a and/or electrode 320 b may comprise (or mayconsist essentially of) a nitrogenated carbon material. The nitrogenatedcarbon material may or may not be in direct contact with the thresholdswitching material. Likewise, in one or more embodiments of theinvention, electrode 320 a and/or electrode 320 b may comprise (or mayconsist essentially of) an electrode material where the electrodematerial consists essentially of the elements carbon and nitrogen. Inone embodiment, the atomic percent of the carbon is greater than theatomic percent of the nitrogen. In other embodiments of the invention,the atomic percentages of the carbon and the nitrogen may be varied asdescribed herein. In the embodiment shown in FIG. 4, the electrodes 320a and 320 b are shown to be in direct physical contact with thechalcogenide threshold switching material. In other embodiments of theinvention, one or both of the electrodes may not be in direct physicalcontact with the threshold switching material.

It is further noted that all of the methods described herein for makingthe electrodes and electrode materials (such as the carbonated nitrideelectrode materials) may be used in combination with threshold switchingmaterials (such as chalcogenide threshold switching materials and S-typethreshold switching materials).

While the present invention has been particularly shown and describedwith reference to the foregoing embodiment, it should be understood bythose skilled in the art that various alternatives to the embodiments ofthe invention described herein may be employed in practicing theinvention without departing from the spirit and scope of the inventionas defined in the following claims. It is intended that the followingclaims define the scope of the invention and that the method and systemwithin the scope of these claims and their equivalents be coveredthereby. This description of the invention should be understood toinclude all novel and non-obvious combinations of elements describedherein, and claims may be presented in this or a later application toany novel and non-obvious combination of these elements. The foregoingembodiment is illustrative, and no single feature or element isessential to all possible combinations that may be claimed in this or alater application. Where the claims recite “a” or “a first” element ofthe equivalent thereof, such claims should be understood to includeincorporation of one or more such elements, neither requiring norexcluding two or more such elements.

1. An electronic device, comprising: a programmable resistance material;and a first electrode in electrical communication with said programmableresistance material, said first electrode comprising carbon andnitrogen; wherein the atomic concentration of carbon in said firstelectrode is greater than or equal to 60% and the atomic concentrationof nitrogen in said first electrode is less than or equal to 40%.
 2. Thedevice of claim 1, wherein the atomic concentration of carbon in saidfirst electrode is greater than or equal to 70% and the atomicconcentration of nitrogen in said first electrode is less than or equalto 30%.
 3. The device of claim 1, wherein the atomic concentration ofcarbon in said first electrode is greater than or equal to 80% and theatomic concentration of nitrogen in said first electrode is less than orequal to 20%.
 4. The device of claim 1, wherein the atomic concentrationof carbon in said first electrode is greater than or equal to 90% andthe atomic concentration of nitrogen in said first electrode is lessthan or equal to 10%.
 5. The device of claim 1, wherein the atomicconcentration of carbon in said first electrode is greater than or equalto 95% and the atomic concentration of nitrogen in said first electrodeis less than or equal to 5%.
 6. The device of claim 1, wherein theatomic concentration of carbon in said first electrode is between 90%and 95% and the atomic concentration of nitrogen in said electrode isbetween 5% and 10%.
 7. The device of claim 1, wherein said firstelectrode consists essentially of nitrogen and carbon.
 8. The device ofclaim 1, wherein said first electrode contacts said phase-changematerial.
 9. The device of claim 1, wherein said programmable resistancematerial comprises a chalcogenide material.
 10. The device of claim 1,wherein said programmable resistance material comprises a phase-changematerial.
 11. The device of claim 1, further comprising a secondelectrode in electrical communication with said programmable resistancematerial.
 12. The device of claim 11, wherein said second electrodecomprises carbon and nitrogen.
 13. The device of claim 12, wherein theatomic concentration of carbon in said second electrode is greater thanor equal to 50% and the atomic concentration of nitrogen in said secondelectrode is less than or equal to 50%.
 14. An electronic device,comprising: an S-type threshold switching material; and a firstelectrode in electrical communication with said S-type thresholdswitching material, said first electrode comprising carbon and nitrogen;wherein the atomic concentration of carbon in said first electrode isgreater than or equal to 60% and the atomic concentration of nitrogen insaid first electrode is less than or equal to 40%.
 15. The device ofclaim 14, wherein the atomic concentration of carbon in said firstelectrode is greater than or equal to 70% and the atomic concentrationof nitrogen in said first electrode is less than or equal to 30%. 16.The device of claim 14, wherein the atomic concentration of carbon insaid first electrode is greater than or equal to 80% and the atomicconcentration of nitrogen in said first electrode is less than or equalto 20%.
 17. The device of claim 14, wherein the atomic concentration ofcarbon in said first electrode is greater than or equal to 90% and theatomic concentration of nitrogen in said first electrode is less than orequal to 10%.
 18. The device of claim 14, wherein the atomicconcentration of carbon in said first electrode is greater than or equalto 95% and the atomic concentration of nitrogen in said first electrodeis less than or equal to 5%.
 19. The device of claim 14, wherein theatomic concentration of carbon in said first electrode is between 90%and 95% and the atomic concentration of nitrogen in said electrode isbetween 5% and 10%.
 20. The device of claim 14, wherein said firstelectrode consists essentially of nitrogen and carbon.
 21. The device ofclaim 14, wherein said first electrode contacts said S-type thresholdswitching material.
 22. The device of claim 14, wherein said S-typethreshold switching material comprises a chalcogenide material.
 23. Thedevice of claim 14, further comprising a second electrode in electricalcommunication with said programmable resistance material.
 24. The deviceof claim 23, wherein said second electrode comprises carbon andnitrogen.
 25. The device of claim 24, wherein the atomic concentrationof carbon in said second electrode is greater than or equal to 50% andthe atomic concentration of nitrogen in said second electrode is lessthan or equal to 50%.